Recent years, the operating temperature of components used in automobiles and industrial equipments has been more and more rising and accordingly, higher heat-resistant cast steels are now being more used. Especially, with the strengthening of exhaust gas regulations, the exhaust gas temperature is becoming higher and higher in the automobiles and industrial equipments or the like and a cast steel with high heat-resistance performance is used for an exhaust system component such as for example, an exhaust manifold of the engine used under the temperature of 900° C. or more.
As the high heat-resistant cast steel, austenitic system heat-resistant cast steel and ferrite system heat-resistant cast steel are exampled. As to the austenitic system heat-resistant cast steel, although the heat-resistance performance is excellent, the material cost is very high due to the high content of expensive nickel and the cutting performance is not so good. On the other hand, as to the ferrite system heat-resistant cast steel, the cost is relatively inexpensive compared to the austenitic system heat-resistant cast steel. However, the heat-resistance performance is not sufficient, considering the recent requirements. Further, the normal temperature toughness of the ferrite system heat-resistant cast steel is not necessarily good and use of the ferrite system heat-resistant cast steel still needs some work in order to gain the high reliability.
In Patent Document 1 (JP 07 (1995)-34204 A), a ferrite heat-resistant cast steel including 0.06% to 0.2% of sulfur to improve cutting performance is disclosed. However, this is still not sufficient.